Spindle drives are known in which the platform is mounted by several bearing devices arranged on it on several axiparallel spindles and can be moved together with the beating devices axially along the spindles and in which one of the spindles is a rotating threaded spindle on which a bearing device having a spindle nut is arranged and one of the bearing devices has radial play to balance the radial threaded spindle eccentricity.
U.S. Pat. No. 4,326,643 (in the name of Bayne, et al; issued Apr. 27, 1982) discloses such a device for vertical lifting and lowering of a stack of flat objects (magnetic cards) in a card delivery machine, in which a platform or container carrying the stack can be moved by a spindle drive having a threaded spindle and a cylinder shaft in the vertical lifting direction and the platform during the lifting movement is guided by the cylinder shaft arranged axiparallel to the threaded spindle and at a spacing from it and secured against horizontal pivoting. The platform is mounted on the threaded spindle by a spindle nut and on the cylinder shaft by a bearing bush.
In order to avoid jamming of the platform against the cylinder shaft caused by the threaded spindle eccentricity or blocking or stiff movement of the platform, the spindle nut is arranged freely moveable in the form of a rectangular block (spherical cap) in a pocket-like bearing cavity (in the region of a U-shaped recess) on one of the sides of the platform loosely, i.e., in a horizontal plane radially around the threaded spindle. The horizontal and radial movement freedom of the spindle nut relative to the platform is slightly greater than the radial eccentricity of the threaded spindle.
A drawback of this disclosed variant is that because of the use of the single threaded spindle for the lifting movement of the platform carrying the stack, in heavy stacks tilting and therefore jamming or clamping of the platform against the cylinder shaft or the threaded spindle can occur. Moreover, high friction forces from surface friction between the spindle nut (spherical cap) and platform in the bearing cavity during horizontal radial movement of the spindle nut against the platform caused by the spindle eccentricity to occur because of the design of the bearing site in heavy stacks, which favor jamming of the platform against the cylinder shaft and causes high material abrasion at the bearing site.